Traveling surfaces such as roads, carriageways and the like are inherently subject to heavy wear from traffic and degradation from weather conditions and ground movements. It is known that wear of the roads foundations typically begins with the cracking of the pavement. This necessitates regular monitoring of the pavement condition to plan maintenance programs.
Fundamental to an effective maintenance and reconstruction program is the acquisition of accurate information concerning the condition of the pavement. At the present such procedures for obtaining this information are very time consuming and labor intensive and are inherently inaccurate and unreliable.
Despite a number of attempts that have been made to develop equipment for testing the condition of the pavement, most public agencies utilize a subjective system of analyzing the condition of the pavement by the human eye by directly viewing the pavement surface or indirectly viewing the pavement through the use of photographs and video that have been taken of the pavement. In the latter process, most often, the photos are analyzed by the human eye to determine the presence and severity of pavement distress features.
In a somewhat similar context, mobile equipment has been devised in the past for determining the roughness of the road or pavement. Indeed, vision systems mountable on a vehicle traveling onto a traveling surface such a road have been developed. However, most existing imaging systems, which use 2D cameras, often suffer from non-uniform lighting and shadows generally caused by the presence of the sun, trees, viaducts, buildings, the inspection vehicle itself or other vehicles as non-limitative examples. With these systems, detection of cracks is neither accurate nor reliable due to the limited resolution of the cameras and the poor contrast of the gathered images. Moreover, because of the presence of the sun, it is challenging task to maintain image quality under this highly variable and uncontrolled light.
For example, known in the art, there is an automated road and pavement condition data collection system proposed by the company Pathway services Inc. which relies on the use of 4 cameras. Two cameras are mounted in front of the vehicle for providing a first set of images while the remaining two cameras are mounted in the back of the vehicle for providing a second set of images. With this particular arrangement, generally, at least one of the two sets of images will not have shadows caused by the inspection vehicle. However, both sets of images may suffer from other shadows coming from surrounding trees, buildings for example. Moreover, this system is quite cumbersome since it relies on the use of a set of camera both in front and rear of the vehicle.
Also known in the art, there is a road inspection system proposed by Fugro-bre Inc. which relies on the use of a digital camera and synchronized strobe lights for inspecting the road. This system is mounted on the rear of a vehicle and is quite cumbersome. Moreover, this system has to operate at night-time to avoid shadows and difficult illumination conditions caused by the sun.
Also known in the art, there is the crack detection system developed by Roadware which uses matrix cameras with strobe lights to allow the system to operate in daytime. The cameras are capable of recording images at speeds up to 50 mph. One major disadvantage of such a configuration is that the angle between the strobe lights and the cameras are a cause a major non-uniformities in the images. This is caused by the fact that the pavement areas that are closer to the strobe lights appear much brighter than those further away, a lighting gradiant is thus created and reduces the quality of the images and contrasts.
Another system known in the art is the road inspection system that was proposed by both Waylink Corporation and International Cybernetics Corporation. Both these systems are provided with a single linescan camera which has to be extended high above the vehicle on which the system is mounted. The system is also provided with a large number of light bulbs in an attempt to produce a powerful uniform light line on the road to be inspected. The major disadvantage of this system is the large quantity of electricity needed, thousands of watts, to power the system. A generator is thus necessary to power the whole system. The whole system is thus cumbersome, and, moreover, it is not able to provide good shadow contrast in the images especially as pertains to longitudinal cracks.
None of the above mentioned inspection systems is adapted to perform a fast enough automatic accurate road inspection immune to surrounding light condition changes while providing a compact and power efficient assembly.
Therefore, it would be desirable to provide a vision system for scanning a traveling surface such as a road to detect surface defects thereof, and which would give optimum crack image contrasts for both transverse and longitudinal cracks, which would be immune to surrounding light condition variations, while being automatic, fast enough, compact and power efficient.